FIG. 1 illustrates a block diagram of a conventional power delivery system 100 for delivering power to a battery 108. As shown in FIG. 1, the power delivery system 100 includes an adapter 102 and a host device 104. The host device 104 includes a power-delivery (PD) interface 142, a power conversion circuit 110 (e.g., a switching charger), a controller 106, and system circuitry. The power conversion circuit 110 includes a switching circuit (e.g., including a high-side switch 112 and a low-side switch 116), an inductor 114, and a filter circuit such as a capacitor 118. In operation, the adapter 102 converts an alternating-current (AC) input voltage VAC to a direct-current (DC) output voltage VDC, and provides the DC voltage VDC to the PD interface 142 of the host device 104. The PD interface 142 delivers the DC voltage VDC to the power conversion circuit 110. The controller 106 controls the power conversion circuit 110 to convert the DC voltage VDC to a charging voltage VCH to charge the battery 108 by alternately switching on the switches 112 and 116. For example, when the switch 112 is on and the switch 116 is off, the inductor 114 receives power VDC from the PD interface 142 and an inductor current IL flowing through the inductor 114 increases. When the switch 112 is off and the switch 116 is on, the inductor 114 releases power and the inductor current IL decreases. The inductor current IL ramps up and down when the controller 106 alternately turns on the switches 112 and 116. The capacitor 118 filters out an AC portion of the inductor current IL and provides a DC charging current ICH to charge the battery 108. The controller 106 can increase the charging current ICH or the charging voltage VCH by increasing the duty cycle of the switches 112 and 116, and decrease the charging current ICH or the charging voltage VCH by decreasing the duty cycle of the switches 112 and 116. As a result, the power delivery system 100 can adjust power delivered to charge the battery 108 at a specified level.
A conventional method to perform fast charge on the battery 108 includes controlling the power conversion circuit 110 to convert the DC voltage VDC to a relatively large charging current ICH to charge the battery 108. However, the power conversion circuit 110 consumes relatively high power when a large current flows through the elements (e.g., including the switch 112, the switch 116, and the inductor 114) in the power conversion circuit 110. It is because these elements include non-zero resistance when they are operating in a switching mode, e.g., in which the switches 112 and 116 are turned on and off alternately. Thus, a conversion efficiency of the power conversion circuit 110 is relatively low. Additionally, in the conventional power delivery system 100, the PD interface 142 has a current limit that defines a maximum level of an input current of the host device 104. In order to generate a relatively large charging current ICH to charge the battery 108, an adapter 102 with a relatively high output voltage VDC is used to provide power to the host device 104. Thus, the voltage across the power conversion circuit 110 is relatively high, which also causes high power consumption in the power conversion circuit 110. Moreover, the power consumption of the power conversion circuit 110 is converted into plenty of heat to increase the temperature of the power conversion circuit 110 and the battery 108, which deteriorates the battery 108 and reduces the lifetime of the battery 108. Furthermore, an inductor (or switch) capable of sustaining a large current and/or a high voltage usually has a large size and is expensive. Thus, the size of a printed circuit board (PCB) for a power conversion circuit 110 including such an inductor 114 and switches 112 and 116 can be relatively large, and the cost for it can also be relatively high. Solutions that address these shortcomings would be beneficial.